A magnetic resonance imaging apparatus is an apparatus that images an inside of a subject by using a magnetic resonance phenomenon. Such magnetic resonance imaging apparatus includes a static magnetic-field magnet that generates a static magnetic field in an imaging area, a gradient magnetic-field coil that applies a gradient magnetic field onto a subject placed in the static magnetic field, and a radio frequency coil that receives a magnetic resonance signal from the subject applied with the gradient magnetic field.
Some of conventional magnetic resonance imaging apparatuses include a shimming unit for correcting ununiformity of a static magnetic field in an imaging area. As an example of such shimming unit, a technology that uses, for example, metal shims formed in a plate shape, is proposed (for example, see JP-A H8-299304 (KOKAI)). According to the conventional technology, ununiformity of a static magnetic field is corrected by stacking in layers and arranging a certain number of metal shims at respective positions in the vicinity of a static magnetic-field magnet.
However, according to the conventional technology described above, the metal shims provided on a gradient magnetic-field coil sometimes move in some cases, resulting in a problem that noise appears on an image due to the movement of the metal shims.
Specifically, while imaging, when a gradient magnetic field is generated by the gradient magnetic-field coil, an eddy current is induced in the metal shims. When a plurality of metal shims is provided, a potential difference arises between each of the metal shims due to the eddy current. In such state, for example, if relative positions of the respective metal shims are changed due to vibration of the gradient magnetic-field coil, as respective metal surfaces are brought close to each other, a weak discharge phenomenon occurs at ends of the metal shims. The discharge phenomenon causes a pop noise, and the pop noise causes noise to appear on a taken image.